This invention generally relates to endodontic therapy systems, apparatuses and methods that make use of bite registration or impression trays. More specifically, the invention relates to a system that helps technicians ideally position a patient's head prior to a cone beam computerized tomography (“CBCT”) capture for the purpose of designing and fabricating drill guides used in minimally invasive implant surgery, root canal treatment, or endodontic surgery.
Endodontic therapy is done to eliminate degenerating pulp tissue and infection from inside dental root structure in order to maintain or return the health of the periodontal supporting structures surrounding said tooth. X-ray imaging allows dentists to visualize the mineralized anatomic structures below the surface of gum and tooth structure to look for signs of decay, failure of previous restorative work, and infection associated with endodontic disease, periodontal disease, or root fractures. Dental radiography, if treatment is needed, also informs the dentist of the morphology of the roots and the root canal systems inside of them. Unfortunately, traditional two-dimensional PA radiographic methodology obscures anatomic detail and dental pathosis due to the superimposition of all bone and tooth structure in a given x-ray plane.
Recently, CBCT has been introduced to dentistry, revolutionizing clinical diagnosis, treatment planning, and treatment execution. The single shortcoming of CBCT imaging is the beam-hardening artifacts that occur adjacent to radio-dense dental materials and objects including but not limited to stainless steel posts in roots, cast-metal crowns, and silver fillings. This artifacted coronal zone (“ACZ”) is generally acceptable to dentists because these are the soft and hard tissues that can be examined directly with adequate light and magnification and because conventional periapical radiographs can often show decay underneath fillings and the margins of crowns.
There are two applications, however, where it is critical to have an accurate representation of the tooth and gingival structures typically obscured in the ACZ of CBCT reconstructions. The first, and the most common, application is when CAD/CAM fabrication of dental prostheses is planned. In that case the external hard and soft tissue contours are captured with analog or digital impressioning methods alone as bone or root structure are not directly related to that treatment plan.
The second application is when drill guides are to be designed and fabricated for minimally-invasive implant surgery, root canal treatment, or endodontic surgery. To accomplish this, an analog or digital impression of the patient's teeth is taken. From this, an acrylic scanning appliance is fabricated on either the plaster model created from a traditional impression or on a polymer model generated from digital impressioning (or scanning a plaster model of the patient's teeth) and 3D printing. The scanning appliance has three or more radiographic registration markers—such as glass beads—attached at various positions around the outward and inward perimeters of the appliance so that the markers that can be easily seen without causing artifacts when the appliance is scanned.
The scanning device is then placed in the patient's mouth, onto their teeth, and a CBCT scan is captured. As usual, in this first volume the teeth and gingiva are obscured in the ACZ. However, the jaws and teeth above and below the ACZ are represented without artifact, as are the registration markers on the inside and outside perimeters of the scanning appliance. Then the appliance is scanned alone, on a stand in the center of the machine's rotational scanning path.
This second (appliance alone) volume is different than the first (in-mouth) volume—it is without artifact, and because the registration markers on the appliance reconstruct without artifact in both volumes, it becomes possible to superimpose the two volumes by aligning the same markers in each. After this the ACZ is subtracted from the first scan of the patient and is replaced with the tooth and gingiva map from the second scan thereby creating, in essence, a holistic digital model of all the patient's soft and hard tissues.
The greatest obstacle to mass market acceptance of CT-guided cutting procedures in dentistry is the time, effort, and expense currently required to create CT-based drill guides for implant surgery. The preferred embodiments of the invention described in this application are an improvement over the prior art as it eliminates the need for a separate laboratory procedure, the cost of that procedure, and the need for a second appointment to complete the imaging. This invention also helps CT technicians ideally position the patient's head prior to the CBCT capture to minimize the height of the artifacted coronal zone and maximize the anatomy seen around that zone. Last, any dental lab or office with 3D printing capability can print the drill guide suggested by the scans.